perf(ivy): cache export scopes extracted from declaration files (#34332)

The export scope of NgModules from external compilations units, as
present in .d.ts declarations, does not change during a compilation so
can be easily shared. There was already a cache but the computed export
scope was not actually stored there. This commit fixes that.

PR Close #34332

packages/compiler-cli/src/ngtsc/scope/src/dependency.ts

@@ -123,9 +123,11 @@ export class MetadataDtsModuleScopeResolver implements DtsModuleScopeResolver {
       throw new Error(`Exported value ${exportRef.debugName} was not a directive, pipe, or module`);
     }
 
-    return {
+    const exportScope: ExportScope = {
       exported: {directives, pipes},
     };
+    this.cache.set(clazz, exportScope);
+    return exportScope;
   }
 
   private maybeAlias<T extends DirectiveMeta|PipeMeta>(